Process of preparing a polyvalent metal soap



Patented Sept. 4, 1951 UNITED STATES PATENT I OFFICE PROCESS OF PREPARING A POLYVALENT METAL SOAP ware No Drawing. Application June 1, 1949, Serial No. 96,628

1 Claims. (01. zen-399i The present invention relates to extreme pres-' sure lubricants and additives therefor, and particularly to the load bearing ingredients designed for use in such lubricants. It relates more especially to oil soluble soaps of polyvalent metals such as the soaps of lead, manganese, zinc. copper, and the like. In particular, it relates to the lead soaps which are suitable for imparting extreme pressure properties to lubrieating oils and greases, but it contemplates also the analogous soaps of other metals which are useful for various other purposes.

It has long been known that ordinary lubricents of petroleum oil derivation are frequently deficient in film strength and load carrying properties. Various additives have been proposed for increasing the film strength or for imparting particular propertiesto the lubricant to render it suitable for lubricating metal surfaces which are subjected to high unit pressures. Whereas ordinary mineral base oils and greases are capable only of bearing loads up to several thousand pounds per square inch, the load bearing capacity of such oils may be increased several fold by adding certain compounds which either strengthen the film or which react with the metals themselves to produce protective films on the metallic surfaces. Among such compounds have been certain metal soaps, especially the lead soaps such as lead oleate and lead naphthenate. Lead oleate is a, fairly effective extreme pressure additive, but it has a low oil solubility which frequently makes it unsuitable, tending to form sludges, and its load carrying capacity is not as high as is desirable for some purposes. The lead naphthenates, while oi satisfactory oil solubility have a definite thinning-out eiiect when compounded into soap thickened greases, requiring excessive amounts of soap thickeners, which is undesirable economically and in service particularly at the lower operating temperatures.

According to the present invention, an improved class of polyvalent metal soaps may be prepared from certain synthetic acid which are prepared in part from aliphatic mercaptans. These aliphatic mercaptans which are usually, though not necessarily, obtained from petroleum oils, as by the H28 treatment of olefins, are reacted with an acidic or acidogenic substance,

2 preferably one containin a double bond such as acrylonitrile CH2ZCHCEN. This general reaction proceeds according to the formulas:

5 RSH-i-CH-.-=CHCEN RSCHzCH2C N and A base such as NaOH may be added to the reactants in each of the formulas to hydrolyze the nitrile as fast as it is formed and thus to prepare a monovalent metal salt directly..

Alternatively, a similar acid product may be made by reacting a material such as betapropiolactone with the mercaptan. This material, unlike acrylonitrile, need not be hydrolyzed and the same type of acid is obtained. In

this case also the salt may be prepared by adding a metal base such as NaOH or KOH.

As a further variation it is possible also to add mercaptans to unsaturated acids like undecylenic acid. The mercaptan used should have at least 8 carbon atoms in order that the salt or soap eventually to be prepared may have requisite oil solubility. As an upper limit, the

mercaptan may have as many as about 20 carbon atoms per molecule. The branched chain mercaptans are preferred because they appear to have superior oil solubility and they form a soap that i plastic and readily workable. The

Co to C12 branched chain mercaptans are par-' ticularly preferred. In some cases. however, the

straight chain type mercaptans may be used.

However, where aliphatic acids of longer chain length are used, the use of shorter chain mercaptans is possible. The total chain length should be not less than about 9 and not more than about 25 carbon atoms.

A suitable acid prepared as above, has the general formula RiSRiCOOH where R1 preferably has from 8 to 20 carbon atoms and R2 is a, short chain. The length of chain R: is preferably from 1 to about 4 or 5 carbon atoms although the more expensive longer chain olefinic acids can be used. At least the total chain length is between about 9 and 25 carbon atoms. This acid is next reacted with 50 a suitable strong base. An alkali metal by droxide such as sodium hydroxide is preferred to produce the salt or soap of this acid. Such a soap is usually at least moderately water soiubleand is dissolved in water. A water soluble salt of the desired polyvalent metal is added to the solution, preferably along with a hydrocarbon in which the resulting soap of polyvalent metal may be soluble.

While the lead salts are preferred for extreme pressure additives because of their good load carrying properties, the salts of other metals such as zinc, manganese, copper, cobalt, calcium, barium or strontium may be used. Zinc soaps of the acids described above appear to have value also as metal corrosion, oxidation, and rust inhibitors in turbine oils and also as grease thickening agents. Some of the others, such as the soaps of copper, cobalt or manganese have utility as fungicides and as paint driers.

The acid prepared from the mercaptan, and the aoidogenic radical as described above, is therefore converted first to a water soluble soap and then by double decomposition to a polyvalent metal soap which, in general, is not water soluble but is soluble in oil. By adding a hydrocarbon to the aqueous soap solution obtained when sodium hydroxide or other strong base is used to neutralize the acid, a water and oil mixture may be maintained by continued agitation and when the polyvalent metal salt, lead acetate for example, is added, the resulting sodium acetate dissolves in the water and the lead soap dissolves in the oil. Thereafter, the hydrocarbon oil, which may be a light naphtha or a heavier hydrocarbon fraction, is allowed to separate from the water and is decanted. The oil solution then may be treated, for example to evaporate the naphtha and recover the polyvalent metal soap, or a part at least of the hydrocarbon may be allowed to remain as a carrier for the soap. If the hydrocarbon oil comprises a lubricating grade of oil, an extreme pressure concentrate may thus be provided directly.

The invention will be more fully understood by reference to the following specific examples:

EXAMPLE I A C12 aliphatic mercaptan, obtained from a petroleum fraction or from any other suitable source, was reacted with acrylonitrile and the nitrlle hydrolyzed with sodium hydroxide to form the sodium soap C12H25SCH2CH2COON a This soap was dissolved in water. Petroleum naphtha was then stirred into the aqueous solution and lead acetate was added, with continued stirring, in sufiicient quantity to fully replace the sodium. Thereafter, the solution was allowed to stand for a few minutes to permit the hydrocarbon solution to separate from the water. The supernatant hydrocarbon was then decanted and the naphtha was then distilled to leave the dry lead soap. The soap was analyzed and found to have a lead content of 24.6%, as compared with a theoretical lead content of 27.5%. The sulfur content was found to be 8.0%, compared with 8.5% theoretical (by weight).

This lead soap was found to be completely soluble in 10% weight concentration in a lubricating oil of naphthenic base having a viscosity of about S. S. U. at 210 F. It was also soluble in the same proportions in a high viscosity index solvent extracted oil; In both cases, it was found to be compatible with calcium base greases and with lithium base greases in at least 15% concentrations by weight.

A 10% oil solution of the lead soap of this exgrlnple did not discolor copper after 3 hours at Metal Anslysis m gm Calculated 30. 8 10. 0 Found 31. l 9. 4

This product was compared with a conventional lead oleate as to load bearing properties and showed some superiority, as indicated in the following table.

Table Timken Tests 0K load Sear load 10% Lead oleate A in calcium base grease 33;? 38# 10? Lead oleate B in calcium base grease 33# 1 a Lead soap, Ex. I., in calcium base greasc 41! 5i# The presence of sulfur in the molecule probably contributes somewhat to the load bearing efiiciency of the additive.

It appears that compositions are most suitable which have the maximum lead content consistent with oil solubility and other requirements. For this reason, where the mercaptan is of long chain and the acid radical short, the mercapta'n preferably should have from 8 to about 12 carbon atoms. As indicated above, compositions prepared from mercaptans of up to 20 carbon atoms, or from acids of up to 25 carbon atoms in total chain length are quite satisfactory although somewhat deficient in lead and sulfur content.

The material of Example 11 had a relatively high proportion of lead because of the short overall chain length and resulting low molecular weight of the organic group. As noted, a Ca mercaptan was used to form the acid.

It will be understood that additives prepared as above may be used in various types of lubricating oils and greases as is common practice in the prior art. They may also be combined with other conventional additives such as soaps to form greases, including carbon blacks and other thickeners, viscosity index improvers, pour point depressors, oxidation inhibitors, metal deactivators, and the like, in the usual conventional proportions.

What is claimed is:

1. The process of preparing a polyvalent metal soap of a sulfur bearing acid which comprises reacting an aliphatic mercaptan with an allphatic acidogenic material, said mercaptan and acidogenic material having a combined chain length of 9 to 25 carbon atoms per molecule to form an acid, neutralizing said acid with an alkali metal base to form a water soluble soap, dissolving said soap in water and adding a, hy drocsrbon oil, adding a water soluble salt of polyvalent metal to form an oil soluble polyvalent soap and separating said soap from said alkali metal salt.

2. Process as in claim 1 wherein the acidogenic material is unsaturated.

3. Process according to claim 1 wherein the ac-idogenic material is acrylonitriie.

4. Process according to claim 1 wherein the acidogenic material is beta-propioiactone.

5. Process according to claim 1 wherein the w polyvalent metal is lead.

6. Process of preparing a polyvalent metal soap of a sulfur bearing acid which comprises combining an aliphatic mercaptan with a Ca to C12 aliphatic acidic material, said mercaptan and said acidic material having a combined chain length of 9 to 25 carbon atoms, preparing the alkali metal salt of such acid, and forming the lead soap of such acid in the presence of lubricating oil by double decomposition with a water soluble lead soap.

'1. Process according to claim 6 wherein the sulfur bearing acid is formed by reacting the allphatic mercaptan with acrylonitrile.

ARNOLD J. MORWAY. PAUL v. SMITH, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Schwartz-Perry, Surface Active Agents, page 29, published 1949 by Interscience Publishers Inc., of New York. 

1. THE PROCESS OF PREPARING A POLYVALENT METAL SOAP OF A SULFUR BEARING ACID WHICH COMPRISES REACTING AN ALIPHATIC MERCAPTAN WITH AN ALIPHATIC ACIDOGENIC MATERIAL, SAID MERCAPTAN AND ACIDOGENIC MATERIAL HAVING A COMBINED CHAIN LENGTH OF 9 TO 25 CARBON ATOMS PER MOLECULE TO FORM AN ACID, NEUTRALIZING SAID ACID WITH AN ALKALI METAL BASE TO FORM A WATER SOLUBLE SOAP, DISSOLVING SAID SOAP IN WATER AND ADDING A HYDROCARBON OIL, ADDING A WATER SOLUBLE SALT OF POLYVALENT METAL TO FORM AN OIL SOLUBLE POLYVALENT SOAP AND SEPARATING SAID SOAP FROM SAID ALKALI METAL SALT. 